Multi-start thread connection for downhole tools

ABSTRACT

An apparatus for transferring rotary power to a consumer in a wellbore includes a rotary power source positioned along a conveyance device and a drive train connected to the rotary power source. The drive train transfers torque from the rotary power source to a consumer. The drive train includes at least two torque transmitting members connected by a multi-start thread connection.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

This disclosure relates generally to oilfield downhole tools and moreparticularly to methods and devices for transferring rotary power to aconsumer.

2. Description of the Related Art

To obtain hydrocarbons such as oil and gas, boreholes or wellbores aredrilled by rotating a drill bit attached to the bottom of a BHA (alsoreferred to herein as a “Bottom Hole Assembly” or (“BHA”). The BHA isattached to the bottom of a drill string, which is usually either ajointed rigid pipe or a relatively flexible spoolable tubing commonlyreferred to in the art as “coiled tubing.” When jointed pipe isutilized, the drill bit is rotated by rotating the jointed pipe from thesurface and/or by a mud motor contained in the BHA. In the case ofcoiled tubing, the drill bit is rotated by the mud motor. BHA's, as wellas other wellbore devices, may often incorporate equipment that requirethe transfer of rotary power from a generator to a consumer; e.g., froma drilling motor to a drill bit. The transfer of such rotary power oftenoccurs across two or more torque transmitting elements such as shafts.

The present disclosure addresses the need for threaded couplings thatprovide enhanced torque transmitting capabilities during the transfer ofrotary power between two or more torque transmitting elements.

SUMMARY OF THE DISCLOSURE

In aspects, the present disclosure relates to an apparatus fortransferring rotary power to a consumer in a wellbore. The apparatus mayinclude a conveyance device configured to be disposed in the wellbore; arotary power source positioned along the conveyance device, the rotarypower source generating a torque; and a drive train connected to therotary power source, the drive train transferring the torque from therotary power source to a consumer. The drive train includes at least twotorque transmitting members connected by a multi-start thread connectionthat has at least two helically wound intertwined threads.

Illustrative examples of some features of the disclosure thus have beensummarized rather broadly in order that the detailed description thereofthat follows may be better understood, and in order that thecontributions to the art may be appreciated. There are, of course,additional features of the disclosure that will be described hereinafterand which will form the subject of the claims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

For detailed understanding of the present disclosure, references shouldbe made to the following detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings, inwhich like elements have been given like numerals and wherein:

FIG. 1 illustrates a drilling system made in accordance with oneembodiment of the present disclosure;

FIG. 2 illustrates a drilling motor assembly using one or more threadedcouplings made in accordance with embodiments of the present disclosure;

FIG. 3A illustrates a two-start thread configuration in accordance withone embodiment of the present disclosure;

FIG. 3B illustrates an end view of a two-start thread configuration inaccordance with one embodiment of the present disclosure; and

FIG. 4 schematically illustrates an end view of a three-start threadconfiguration in accordance with one embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to devices and methods for enhancedthreaded connections between a driving rotating member and a drivenrotating member. Threaded connections for torque transmission from onecomponent to another can become damaged if over-torqued. To increase thetorque capacity, the present disclosure uses a multi-start thread toreduce the induced shoulder load between two threaded components for agiven torque. Additionally, the “make-up” and “break up” may be fasterfor such threaded connections. The present disclosure is susceptible toembodiments of different forms. The drawings show and the writtenspecification describes specific embodiments of the present disclosurewith the understanding that the present disclosure is to be consideredan exemplification of the principles of the disclosure, and is notintended to limit the disclosure to that illustrated and describedherein.

In FIG. 1, there is shown an embodiment of a drilling system 10utilizing a bottomhole assembly (BHA) 60 configured for drillingwellbores. While a land system is shown, the teachings of the presentdisclosure may also be utilized in offshore or subsea applications. InFIG. 1, a laminated earth formation 11 is intersected by a wellbore 12.The BHA 60 is conveyed via a drill string 22 into the wellbore 12. Thedrill string 22 may be jointed drill pipe or coiled tubing, which mayinclude embedded conductors for power and/or data for providing signaland/or power communication between the surface and downhole equipment.The BHA 60 may include a drill bit 62 for forming the wellbore 12. Insome embodiments, the BHA 60 may include one or more rotary powersources such as a drilling motor 120.

In a common mode of operation, a pressurized drilling fluid is pumpeddown to the BHA 60 from the surface via the drill string 22. Thisflowing drilling fluid may be utilized to energize the drilling motor120, which generates rotary power that rotates the drill bit 62. Theflowing drilling mud can also energize turbines or other similar devicesthat extract energy from the flowing drilling fluid. The extractedenergy may be utilized to generate electricity and/or pressure hydraulicfluids. It should be understood that generating rotary power (i.e.,generating useful torque) and electrical power generation and pressuringof fluids are merely illustrative of a variety of functions that may beperformed by a consumer of rotary power.

Referring now to FIG. 2, there is shown in greater detail one embodimentof a drilling motor 120 that may be used with the BHA 60 (FIG. 1). Thedrilling motor 120 is a positive displacement motor that includes arotor 122 disposed in a stator 124 forming progressive cavities 123there between. Fluid supplied under pressure to the motor 120 passesthrough the cavities 123 and rotates the rotor 122. The rotor 122 inturn is connected to the drill bit 62 (FIG. 1) via a drive train 125that is formed of two or more interconnected torque transmittingmembers. In one embodiment, the drive train 125 includes a flex shaft126 connected to a drive shaft 128 at a pin and box connection 130. Thedrive train 125 may have a greater or a fewer number of these torquetransmitting members.

The drive train 125 can transmit torque from the motor 120 to the drillbit 62 (FIG. 1) using one or more threaded connections. These threadedconnections may be used between the rotor 122, the universal joint (e.g.flex shaft) 126, and the drive shaft 128. In certain embodiments, thedrive train 125 may also include a rotor adapter and bonnet (not shown)and a segmented drive shaft having upper and lower sections. Threadedconnections may also be used transmit torque along these components aswell.

Referring to FIG. 3A, the threaded connection may include a pin end 150and a box end 152 (shown in hidden lines). In a conventional manner, thepin end 150 has external threads and the box end 152 has internalthreads (not shown). The pin end 150 and the box end 152 have abuttingshoulders 154, 156, respectively. When the threaded connection istorqued up to a desired value when the pin end 150 and box end 152 areconnected (i.e., made up), an axial loading occurs at the shoulders 154,156. The ratio between a shoulder load and a make-up torque (MUT)depends on thread geometry. If the transmitted torque is higher thanMUT, then the connection becomes over-torqued resulting in shoulder orpin damage.

In embodiments, the threaded connections of the drive train 125 (FIG. 2)may use a multi-start thread to reduce the induced shoulder load for agiven torque. Reducing the shoulder load may increase the torquecapacity of the connection and may therefore avoid the necessity of adouble shouldering of a connection. An additional advantage is thefaster make and break of long thread cylindrical connections like at thebonnet of a motor. A traditional thread, which is a single start thread,has one helically wound thread. A multi start screw has two or moreintertwined threads. The FIG. 3A thread embodiment has two intertwinedthreads, 158 and 159. The intertwined threads may be helically woundthreads. In these screw configurations, the effective pitch is equal tothe pitch of a standard thread multiplied by the number of starts.

It should be understood that the drill bit is only one illustrativeconsumer of rotary power. Other consumers include, but are not limitedto, under-reamers, reamers, pipe cutting tools, etc.

The number of thread starts may vary depending on application. Thus, theratio between a make-up torque and a break out torque may also varysignificantly. FIG. 3B shows an end view of a two-start thread that hasintertwined threads, 158, 159. FIG. 4 show the end view of a three startthreads having three intertwined threads, 160, 162, 164. While only upto three thread starts are shown, the number of thread starts may beeven higher. The ultimate number of thread starts is reached for aninfinite pitch resulting in a pure spline connection. For a relativelyhigh number of thread starts (e.g., five or more depending on pitch anddiameter), a potential loss of self locking capability may be addressedwith supplemental locking features. Nevertheless, these relatively highthread starts may still be able to transmit bending loads and apply apre-load (clamping force) on components.

The foregoing description is directed to particular embodiments of thepresent disclosure for the purpose of illustration and explanation. Itwill be apparent, however, to one skilled in the art that manymodifications and changes to the embodiment set forth above are possiblewithout departing from the scope of the disclosure. It is intended thatthe following claims be interpreted to embrace all such modificationsand changes.

What is claim is:
 1. An apparatus for transferring rotary power to aconsumer in a wellbore, comprising: a conveyance device configured to bedisposed in the wellbore; a rotary power source positioned along theconveyance device, the rotary power source generating a torque; and adrive train connected to the rotary power source, the drive traintransferring the torque from the rotary power source to a consumer,wherein the drive train includes at least two torque transmittingmembers connected by a multi-start thread connection.
 2. The apparatusof claim 1, wherein the multi-start thread connection is formed at a pinand box connection between the at least two torque transmitting members.3. The apparatus of claim 1, wherein a number of starts of themulti-start thread connection is selected to increase torque capacity ofa connection between the at least two torque transmitting membersrelative to a single start thread connection.
 4. The apparatus of claim1, wherein the rotary power source is a drilling motor.
 5. The apparatusof claim 1, wherein the consumer is a drill bit.
 6. The apparatus ofclaim 1, wherein at least one of the two torque transmitting members isone of: (i) a rotor, (ii) flex shaft, and (iii) a drive shaft.
 7. Theapparatus of claim 1, wherein the conveyance device is a drill string.8. The apparatus of claim 1, wherein the multi-start screw has at leasttwo intertwined helically wound threads.
 9. A method for transferringrotary power to a consumer in a wellbore, comprising: disposing aconveyance device in the wellbore, the conveyance having a rotary powersource generating a torque; and transferring torque from the rotarypower source using a drive train, wherein the drive train includes atleast two torque transmitting members connected by a multi-start threadconnection.
 10. The method of claim 9, wherein the multi-start threadconnection is formed at a pin and box connection between the at leasttwo torque transmitting members.
 11. The method of claim 9, wherein anumber of starts of the multi-start thread connection increases torquecapacity of a connection between the at least two torque transmittingmembers relative to a single start thread connection.
 12. The method ofclaim 9, wherein the rotary power source is a drilling motor, theconsumer is a drill bit, and wherein at least one of the two torquetransmitting members is one of: (i) a rotor, (ii) flex shaft, and (iii)a drive shaft.
 13. The method of claim 9, wherein the multi-start screwhas at least two intertwined threads.
 14. A system for transferringrotary power to a consumer in a wellbore, comprising: a drill stringconveyed into the wellbore; and a bottomhole assembly connected to thedrill string, the bottomhole assembly including: a drilling motorenergized by a drilling fluid circulated in the wellbore, and a drivetrain connected to the rotary power source, the drive train transferringthe torque from the rotary power source to a consumer, wherein the drivetrain includes a multi-start thread formed at a pin and box connectionbetween at least two torque transmitting members.
 15. The system ofclaim 14, the at least one of the two torque transmitting membersinclude a rotor, a flex shaft, and a drive shaft interconnected to oneanother.
 16. The system of claim 14, wherein the number of starts of themulti-start thread is selected to reduce the transmitted torque to avalue lower than the make-up torque.
 17. The system of claim 14, whereinthe multi-start screw has at least two intertwined threads.